Geochemical exploration



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xa sdamosa 3,149,068 GEOCHEMICAL EXPLORATION Edwin W. Biederman, .l'r.,and Bennie Heinze, Tulsa,

flkla, assignors to Cities Service Research and Development Company, NewYork, N.Y., a corporation of New Jersey No Drawing. Filed'Mar. 8, 1961,Ser. No. 94,168 5 Claims. (Cl. 210-31) the presence of petroleumconstituents in earth a rpples snwuock sarpplgnto ascertain the locationand proximity of petroleum deposits by correlating the relative amountsof petroleum constituents present in the earth samples with thelocations from which the samples were taken.

it has been suggested previously that the presence of petroleumconstituents in an earth sample may be detected by extracting organicconstituents from the earth sample and then evaluating the fluorescenceof the extract or a concentration thereof under ultraviolet light. Thesemethods depend upon the known fluorescence of certain petroleumconstitutents, especially intermediate aromatics. One such method isdescribed in US. Patent 2,451,883. While methods of this type fordetermining the presence of petroleum constituents by fluorescence ofearth samples or concentrated extracts thereof have met with some degreeof success, such methods have frequently failed to provide the desiredinformation because it has been im possible to distinguish thefluorescence due to the desired petroleum constituents from fluorescencedue to other organic constituents.

While certain petroleum constituents, especially the lighter aromaticsnormally found in petroleum, fiuoresce strongly in the light blue rangeunder ultraviolet radiation, numerous other organic compounds which donot necessarily indicate the presence of petroleum (although they mayalso be present in petroleum) also fluoresce under ultraviolet light,some of them in the same color range. For instance, extracts of coals,coal-like materials and chlorophylls all fluoresce under ultravioletlight but are not an indication of the presence of petroleum. Morespecifically, anthracene type materials fluoresce with a light bluecolor and are readily extracted from soft coal and anthracite. Where theanthracene is oxygenated and occurs as anthraquinone, it also fluorescesblue. Organic'acids and cresols likewise contribute to the overallfluorescence of earth samples. Crude oils, however, contain much less ofthese materials than do shales, especially oil barren shales. If asufiiciently strong solvent is used to extract substanti ly all of thedesired petroleum constituents, then an of these undesirable fluorescentorganic constituents present in the sample will be extracted along withthe desired petroleum constituents. Previously known methods fordetermining the presence of petroleum constituents by fluorescence ofearth samples or extracts theretrorn have been unable to discriminatebetween the various types of fluorescent materials mentioned above.

It is an object of the present invention to provide an improved methodof geochemical exploration to determine the proxitriity of petroleumdeposits.

Another object of the invention is to provide a novel method fordetecting the presence of petroleum constituents in earth samples.

It has now been found that the presence of petroleum constituents inearth samples may be determined with a high degree of accuracy by firstapplying chromatographic separation techniques to separate from theearth sample those constituents which are not mobile in polarchromatographic carrier solvents but which are mobile in non-polarchromatographic carrier solvents. The fluorescence of these constituentsis then checked to determine the presence of fluorescentpetroleumconstituents in the earth sample.

Any suitable chromatographic technique may be used in separatingconstituents of earth samples in accordance with the persent invention.For instance, the separation may be efiected in a combination ofchromatographic columns packed With suitable chromatographic adsorptionmaterial such as cellulose, alumina gel, silica gel, etc. While columnchromatography or suitable combinations of other one dimensionalchromatographic techniques may be used, it is highly advantageous toutilize two dimensional chromatography in obtaining the desiredseparation of constituents from the earth samples. In two dimensionalchromatography, the sample being analyzed is placed on alromatographicadsorption material and driven in two different directions by twodifferent carrier solvents. Due to their difi'erent adsorptioncharacteristics with respect to the adsorption material and solvents,the various constituents of the sample are carried varying dis tancesalong the adsorption material in each direction before being depositedthereon from solution with the carrier. While any suitable bed ofchromatographic adsorption material may be used, the use of a relativelythin layer of material is preferred. Special chromatographic paper orordinary filter paper is especially suitable for this purpose.Two-dimensional chromatography using a relatively thin layer ofchromatographic adsorbtion material such as filter paper is preferred inpracticing the present invention for two reasons. First, this techniquerequires extremely small quantities of extract sample and can thus beused to analyze small earth samples. This, of course, facilitatescollection and transportation of samples as well as analysis and storageof samples and completed chromatograms. In addition, this technique,especially in the form described below, is very simple and readilyadaptable to field conditions, requiring only a minimum I of simple,rugged equipment and small quantities of supplies.

In applying two dimensional chromatography to the practice of apreferred embodiment of the-present invention, the earth sample beinganalyzed is first treated with suitable solvent to extract organicconstituents including the desired petroleum constituents therefrom.This extract is then deposited on chromatographic adsorption materialsuch as ordinary filter paper and the solvent is preferably at leastpartially evaporated. A polar chromatographic carrier solvent is thenintroduced into the adsorption material and passes therethrough byadsorption. Constituents mobile in the polar carrier solvent are thusseparated from the deposited extract and moved along the adsorpitonmaterial in the direction taken by the carrier. A non-polar carriersolvent is then introduced into the adsorption material so as to passthrough the adsorption material in a direction perpendicular to thepath'of the polar solvent. The non-polar solvent thus moves constituentsof the deposited extract which are mobile in the non-polar solvent alongthe adsorption material in the direction of movement of the non-polarsolvent. The fluorescence of any of the thus separated constituents ofthe earth sample may then beevaluated by suitable means such as the useof a standard ultraviolet light. It should be understood that either thepolar or the non-polar solvent may be used first so long as the secondsolvent passes through the adsorption material in a direction nonparallel and preferably perpendicular to the direction of movement ofthe first solvent. While the order in which the polar and nonpolarsolvents are employed is not critical, it has been found that somewhatsharper separations of various constituents are obtained when the polarsolvent is used first and the use of a polar carrier solvent followed bya nonpolar carrier solvent as described above is, therefore, preferred.

As a matter of convenience in using the two dimensional chromatographictechniques described above and in discussing the results obtained withsuch techniques it has been found desirable to deposit the extractedorganic constituents of the earth sample on thecorner of a square orrectangular piece of filter paper and arbitrarily refer-to the variousportions of the filter paper with reference to the position of thefilter paper when the deposited extract is in the lower right handcorner thereof. This practice will be followed herein.

A wide variety of organic solvents are suitable for ex tracting organicconstituents from earth samples in the practice of the presentinvention. It is preferred, however, to use solvents sufliciently strongto insure that all of the desired fluorescent petroleum constituents areextracted from the sample. If all these constituents are not extracted,the quantitative analytical results will, of course. be son-avhat inerror. To insure that substantially all of the constituents areextracted, the organic solvent used is preferably one which issufficiently strong to dissolve asphaltic material. These may bereferred to as strong organic solvents. For this purpose asphalticmaterial may be defined as hydrocarbon material which is not soluble inpentane. Suitable strong solvents include, for instance, benzene,toluene, xylene, carbon tetrachloride, diethyl ether, ethyl acetate,etc. or combinations of these with polar solvents such as isopropylalcohol or acetone.

Likewise, any suitable polar and non-polar carrier solvents may be usedin practicing the present invention. In order to cause all of thedesired constituents to migrate without having an excessive amount ofthe relatively heavier asphaltlc material migrate, it is preferred thatboth the polar and non-polar carriers be relatively weak carriers whichare not suificiently strong to cause migration of asphaltic material asdefined above. These may be referred to as Weak polar and non-polarcarrier solvents. Use of overly strong carrier solvents tends to causemigration of asphaltic material which then masks the presence of thedesirable constituents, especially the lighter aromatics. Suitable weakpolar carrier solvents include, for instance, methanol, ethanol, acetoneor mixtures of these with small amounts of water.

Suitable non-polar carrier solvents include, for instance, straightchain hydrocarbons having at least 5 carbon atoms, branched chainparaffins. cycloparaffins, etc. Among the polar carrier solventsmethanol has been found especially suitable While among the non-polarcarrier solvents hexane, heptane and octane have been found especiallysuitable.

When organic constituents extracted from earth samples are deposited onthe corner of a sheet of filter paper as described above and the polarcarrier solvent is intro duced by lacing the lower edge of the filterpaper in the solvent so s to cause the same to move upwardly through thefilter paper and the non polar carrier solvent is then introduced byplacing the right hand edge of the filter paper in the non-polar carriersolvent so that it moves to the left across the filter paper, then thedesired fluorescent petroleum constituents which are mobile in thenon-polar solvent but immobile in the polar solvent will be found alongthe lower edge of the filter paper or chromatogram. It is obvious thatthe distance from the original deposit at which these cpnstituents willbe found depends upon the amount and concentration of the carriersolvent uti- 4. lized as well as on the relative adsorptioncharacteristics of the solvent and of the specific constituents. Thefollowing description of various constituents found in various cornersof squares of filter paper following analysis of the type describedabove is based on the assumption that sufficient quantities of carriersolvents are utilized to drive the majority of such compounds which aremobile in the particular solvent involved substantially the entire widthof the filter paper. If the analysis is carried out in this fashion thevarious constituents will be grouped substantially at the corners of thefilter paper. The following compounds are typical of those which will befound at the various corners of the filter paper when the requiredchromatographic separation has been accomplished in the arbitrary mannerdescribed above using methanol as the polar carrier solvent and heptaneas the non-polar carrier.

UPPER LEFT Anthracene Phenanthrene f I l i i J AcenaphtheneAcenaphthylene l l I Q Pyrene Dihydropyrene Tetrahydropyrene CholesterolI CH3 1110112025 CH: (lJH I p i Ca CH3 Ho Stigmasterol CHCH=CH CH: CH: l(I: l f {:Qcm W HO p-Toluidine Methanol mobile heptane immobile fractionof crude oil Methanol mobile heptane immobile fraction of shale extractLOWER LEFT Tetradecane CH;(CH=)1;CH

Hexadecane 0153mm) CH:

Eicosane CH1 (CH-9150B;

Squalane v 011 CH, CH3

Nujol heavy mineral oil Average mol. wt. 547

9,10 dihydroanthracene 1,2-benzathracene Aldrich Chemical Fluoranthene3,4-benzofiuoranthene 1,12-benzoperylene Fluorene Chrysene l l iTriphenylene Cholestane A OH:

GHCILCH, CH| 1 5H: l/ g I CE cg \CH.

9 Perhydropyrene LOWER RIGHT p-Terphenyl Coronene I It i I ll I Byapplying the chromatographic separation techniques described above to anumber of earth samples taken from selected locations it is possible tocorrelate the presence and quantity of petroleum constituents found ineach sampie with the location from which the sample was taken in orderto determine the presence and proximity of petroleum bearing shale orsand, with respect to such location. respect to a number of samples fromthe same general area it is necessary only that the different samples besubjected to the same treatment. any quantitative meaning it is alsonecessary to have available comparative chromatograms based on knownpetroleum bearing formations. By preparing sets of standard izedchromatograms using an arbitrarily standardized technique of the typedescribed above and utilizing earth samples from known locations inreference to known petroleum deposits, it is possible to compare thefluoresence of the appropriate portion of the chromatograms obtainedfrom the earth samples in question with the reference chromatograms inorder to obtain quantitative data respecting the presence of petroleumdeposits in the area from which the samples in question were taken. Forbest results fresh reference standards should be prepared at frequentintervals, preferably weekly, because the lighter aromatics in thefluorescent petroleum fraction exhibit decreasing fluorescence withtime.

Example 1 In the practice of previously known geochemical methods fordetermining the presence of oil constituents in earth samples byfluorescence. oxygen containing compounds have been responsive for muchof the confusion between fluorescent petroleum constituents and otherfluo rescent constituents of the earth samples. border to demonstratethat the method of the present invention separates these compounds frompetroleum constituents, a sample of crude oil containing both oxygenatedcom pounds and petroleum constituents not containing oxygen wasfractionated into 65 fractions by column chromatography using a seriesof carrier solvents (e.g., petroleum ether, benzene, CCl acetone, etc.).Each of these fractions was then subjected both to infrared spectraanalysis and to chromatographic separation using methanol carriersolvent (a polar carrier). In every case where an oxygen band wasobserved in the infrared pattern, a fluorescent fraction mobile inmethanol was observed on the For the results to have relative meaningwith For the results to have 10 chromatogram. Conversely, every casewhere there was no indication of oxygen in the infrared pattern, therewas no fluorescent methanol mobile fraction on the chromatogram.

Detection of fluorescent peh'oleum constituents in accordance with thepresent invention is not, therefore, confused by the presence ofoxygenated compounds in'the earth sample.

Example 2 To further evaluate the method of the present invention. earthsamples from a number of known formations were analyzed by the followingprocedure: In each case the earth sample was pulverized with a mortarand pestle (so that all of the sample passed through a size 50 sieve(U.S. sieve series). Two grams of this material were placed in a smallscrew cap vial and 2 milliliters of a 1:1 solution of isopropyl alcoholand toluene were added with a pipette. The sample vial was then cappedtightly, shaken vigorously for 1 minute and allowed to settle at roomtemperature. Best results were obtained when the vials were agitated 3times in 24 hours, with care being taken after the third agitation towash the sediment fi'om the sides of the vial to insure that all solidswere in contact with the solvent. The sample was then allowed to settleuntil the solution above the sediment was clear. of a milliliter of theextract was then drawn into a micropipette and evaporated onto thecorner of a 1 inch square piece of chromatographic paper (Whatrnan No.1). The margins of the corner spot were confined to an area 5millimeters on a side. A gentle air stream directed onto the area ofevaporation was found to be helpful in speeding up the evaporation ofthe solvent. One edge of the 1 inch square paper containing theevaporated spot of extract (the lower edge according to the arbitraryprocedure discussed above) was then placed in methanol and the methanolwas allowed to migrate upwardly for a distance or" /2 inch. The paperwas then dried in air and the other edge containing the spot (the righthand edge) was placed in heptane which was allowed to migrate at rightangles to the methanol migration. The effect of this was to separate theextract constituents in the manner discussed above with fluorescentpetroleum constituents mobile in heptane (non-polar carrier solvent) butimmobile in methanol (polar carrier) spread out along the bottom edge ofthe paper. After the paper was dry it was examined under a highintensity ultraviolet light (3660 A.) and the intensity of thefluorescence on various portions of the paper was noted and interpretedas described above. In the case or" known oil bearing formations thefluorescence of the fluorescent petroleum constituents was compared withreference standards prepared from related crude oils. In addition, eachof the earth samples tested was also tested in accordance with the priorart techniqum by examining the total extract from the earth sample underthe same ultraviolet light.

When tested by mere examination of total extract under ultra-violetlight as described above and suggested by the prior art, earth samplesfrom each of the following formations (known to contain little or nopetroleum hydrocarbons) exhibited strong fluorescence.

Further analysis of these samples in accordance with the presentinvention and as described above indicated, how: ever, that thefluorescent constituents of these samples were not petroleumconstituents.

Earth samples from the following rock formations were also analyzed asdescribed above.

In each case the extracts from these earth samples fluoresced stronglywhile analysis in accordance with the present invention disclosed thatthe fluorescent material was actually composed partly of fluorescentpetroleum constituents and partly of fluorescent constituents notindicating the presence of petroleum. This was in accordance with knownfacts concerning these formations. In the case of these earth samplesmere examination for fluorescence correctly indicated the presence ofpetroleum constituents but gave completely erroneous informationconcerning the relative quantities of such constituents since, except bythe application of the present invention, it was impossible to determinehow much of the fluorescence was attributable to petroleum constituentsand how much to non-petroleum indicating constituents.

The above examples indicate clearly that the process of the presentinvention is capable of distinguishing between those fluorescentconstituents of earth samples which indicate the presence of petroleumand those fluorescent constituents which may or may not be present inpetroleum but which do not necessarily indicate the presence ofpetroleum.

While the invention has been described above in connection with certainpreferred embodiments thereof, it will be understood by those skilled inthe art that various changes and modifications may be made withoutdeparting from the spirit and scope of the invention and it is intendedto cover all such changes and modifications in the appended claims.

We claim:

1. A geochemical exploration method for determining the proximity of anunderground petroleum reservoir which comprises collecting earth samplesfrom various locations in an exploration zone. similarly and separatelytreating said samples by contacting them with strong organic solvent toextract organic constituents including desired petroleum constituentstherefrom, chromatographically fractionating each sample to separatetherefrom fluorescent petroleum constituents mobile in a weak nonpolarcarrier solvent and immobile in a weak polar carrier solvent, subjectingthus separated constituents to utraviolet radiation, and correlating therelative fluorescence of the fluorescent petroleum constituentsseparated from each sample with the locations from which such sampleswere 60 taken.

2. The method for separating fluorescent petroleum 12 constituents whichare mobile in a weak non-polar chromatographic carrier solvent andimmobile in a weak polar chromatographic carrier solvent from an earthsample containing the same which comprises contacting the earth samplewith :1 strong organic solvent to extract organic constituents includingthe desired petroleum constituents therefrom, depositing thus extractedorganic constituents on chromatographic adsorption material, andtreating thus deposited organic material with a weak polar and anonpolar carrier solvent by first passing one of said carrier solventsin one direction through the adsorption material to thereby separatefractions of the organic constituents mobile in such carrier and thenpassing the second of said carriers through the chromatographicadsorption material in a direction non parallel to the path of the firstof said carriers to thereby separate fractions mobile in said secondcarrier.

3. The method according to claim 2 in which the organic solvent is amixture of isopropyl alcohol and acetone, the polar solvent is methanoland the non-polar solvent is heptane. 1 Y

4. The method for separating fluorescent petroleum constituents whichare mobile in a weak non-polar chro matographic carrier solvent andimmobile in a weak polar chromatographic carrier solvent from an earthsample containing the same which comprises contacting the earth samplewith a strong organic solvent to extract organic -constituents includingthe desired petroleum constituents therefrom, depositing thus extractedorganic constituents on chromatographic adsorption material, andtreating thus deposited organic material with a weak polar and a weaknon-polar carrier by first passing one of said carriers in one directionthrough the adsorption material to thereby separate fractions of theorganic constituents mobile in such carrier and then passing the secondof said carriers through the chromatographic adsorption material in adirection generally perpendicular to the path of the first of saidcarriers to thereby separate from said first fractions those fractionsmobile in said second carrier.

5. The method of determining the presence of fluorescent petroleumconstituents in an earth sample containing the same and otherfluorescent organic constituents which comprises contacting the earthsample with a strong organic solvent to extract organic constituentsincluding the desired petroleum constituents and other undesiredfluorescent constituents therefrom, depositing thus extracted organicconstituents on chromatographic adsorption material, passing a weakpolar chromatographic carrier solvent through said adsorption materialin one direction to thereby separate from the deposited organicconstituents fractions mobile in said polar carrier, passing a weaknon-polar chromatographic carrier solvent through said adsorptionmaterial in a direction generally perpendicular to the path of the polarcarrier to thereby separate fractions mobile in the non-polar carrierand subjecting thus separated fractions to ultraviolet radiation.

Larsen Nov. 25, 1947 Coggeshall et al. Oct. 16, 1956 UNIT D STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3 149 068 September15 1964 Edwin W. Biederman, Jr 7 et ale It is hereby certified thaterror appears in the above numbered petent requiring correction and thatthe said Letters Patent should readas corrected below Column 9 line 34,after "of" insert petroleum deposits such as reservoirs or line 61 for"responsive" read responsible Signed and sealed this 12th day of January1965.

(SEAL) Y Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. A GEOCHEMICAL EXPLORATION METHOD FOR DETERMINING THE PROXIMITY OF ANUNDERGROUND PETROLEUM RESERVOIR WHICH COMPRISES COLLECTING EARTH SAMPLESFROM VARIOUS LOCATIONS IN AN EXPLORATION ZONE, SIMILARLY AND SEPARATELYTREATING SAID SAMPLES BY CONTACTING THEM WITH STRONG ORGANIC SOLVENT TOEXTRACT ORGANIC CONSTITUENTS INCLUDING DESIRED PETROLEUM CONSTITUENTSTHEREFROM, CHROMATOGRAPHICALLY FRACTIONATING EACH SAMPLE TO SEPARATETHEREFROM FLUORESCENT PETROLEUM CONSTITUENTS MOBILE IN A WEAK NONPOLARCARRIER SOLVENT AND IMMOBILE IN A WEAK POLAR CARRIER SOLVENT, SUBJECTINGTHUS SEPARATED CONSTITUENTS TO UTRAVIOLET RADIATION, AND CORRELATING THERELATIVE FLUORESCENCE OF THE FLUORESCENT PETROLEUM CONSTITUENTSSEPARATED FROM EACH SAMPLE WITH THE LOCATIONS FROM WHICH SUCH SAMPLESWERE TAKEN.